Grinding machine

ABSTRACT

A grinding machine in which the grinding cycle is controlled by a stepping motor which receives pulses from a linear feed-controlled generator and which is operative to give an adjustable diamond clearance.

BACKGROUND OF THE INVENTION

It has been common practice, particularly in the case of internalgrinding machines, to operate the cross-feed portion of a grinding cycleby use of an electrical stepping motor which is energized by electricalpulses. The pulses are produced by a pulse generator and a controloperates between the generator and the stepping motor to present thestepping motor with the pulses in various modes, frequencies, andamounts. This makes it possible to select from an almost endless varietyof grinding cycles. Because the counting equipment available forcounting the pulses is so reliable, it is possible to operate thegrinding machine on the "dead reckoning" principle (as it is called inthe art of the ocean navigation), rather than to take readings atcertain intervals to determine the location of the grinding wheelrelative to the workpiece. Such controls for the pulses have had someshortcomings however and one problem is that, when a setting of the feedrate is made on the face of the grinding machine, the setting devicemust consist of a warped potentiometer or a calibrated form ofpulse-rate control. This is because in the past an equal change inresistance at the face of the control box results in a non-linear orexponential change in the frequency output of the generator. Anotherdifficulty that has been experienced is that, as the diamond begins towear, the fact that the infeed distance begins to change becomestroublesome. For instance, in an "interrupt to dress" cycle, the wheelis backed off from the workpiece far enough so that the wheel can passover the diamond for a dress. After the dressing operation is finished,sufficient pulses are introduced into the grinding wheel to advance itinto contact with the workpiece again for the finish grind. As the wheelwears, this advance or diamond clearance is too small and the wheel isliable to strike the workpiece while it is moving at a fairly rapid rateand can cause damage. Therefore, the ordinary operator must set up his"diamond clearance" or index large enough so that this will not happeneven when the diamond wears. Such a large diamond clearance means thatthe machine converts to a slower rate of feed long before the wheelreaches the workpiece and this is a waste of machine time. These andother difficulties experienced with the prior art devices have beenobviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide agrinding machine using the stepping motor feed in which the pulse rateand, therefore, the feed can be closely and easily controlled.

Another object of this invention is the provision of a grinding machinehaving an adjustable diamond clearance, which clearance is adjusted inaccordance with the wear on the diamond.

A further object of the present invention is the provision of aninternal grinding machine of the stepping-motor type in which thefrequency of the electrical pulses presented to the stepping motor forfeed and the number of such pulses presented for diamond clearancepurposes are carefully regulated.

It is another object of the instant invention to provide a grindingmachine whose grinding cycle over a large number of workpieces averagesout to a lesser amount of time than in the prior art.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

SUMMARY OF THE INVENTION

In general, the invention consists of a grinding machine for generatinga surface of revolution on a workpiece, which machine has a base with aworkhead and a wheelhead mounted thereon for relative movementtransversely of the axis of the surface of revolution. A stepping motoris operative to produce the said relative movement in response to thereceipt of electrical pulses and a pulse generator is connected to thestepping motor to supply the said electrical pulses. A resistance unitis connected to the pulse generator to control the frequency of thepulses, the unit including an acutator movable in increments to connectequal increments of resistance to the generator, the said increments ofresistance producing equal increments of frequency of pulses.

A dresser carrying a diamond is mounted on the workhead and means isprovided for generating a signal indicative of wear on the diamond.Means is provided normally introducing a selected number of pulses tothe feed means to produce an original diamond clearance movement betweenthe workpiece and the abrasive wheel. Means is also provided forconverting the signal indicative of wear to a series of pulses andadding them algebraically to the diamond clearance movement after eachdressing operation to bring the dressed surface of the wheel to the samepoint relative to the workhead.

More specifically, a circuit is provided that reduces the pulsefrequency to zero when an open circuit occurs in the resistance unit. Astraight line relationship exists between the resistance in theresistant unit and the frequency of pulses emitted by the pulsegenerator. The means generating a signal indicative of wear is a gagewhich is operative on the surface of the workpiece. The means normallyintroducing a selected number of pulses to the feed means is athree-digit bi-directional electro-mechanical counter with an electricalreadout of each digit. A WORN DIAMOND signal is generated when theresult of the algebraic addition falls below a predetermined value andthe machine is shut down.

BRIEF DESCRIPTION OF THE DRAWINGS

The character of the invention, may be best understood by reference toone of its structural forms, as illustrated by the accompanyingdrawings, in which:

FIG. 1 is a perspective view of a grinding machine embodying theprinciples of the present invention,

FIG. 2 is a transverse vertical sectional view of a portion of themachine,

FIG. 3 is a hydraulic schematic showing the main operating cylinders andsolenoid valves in the machine,

FIG. 4 is a perspective view of the control box with the front open toshow the logic circuit boards,

FIG. 5 is a diagrammatic view of a typical grinding cycle using thepresent invention,

FIG. 6 is a diagrammatic view of the relationship between the grindingwheel, the workpiece, and the diamond dresser in the present invention,

FIGS. 7-15 are electrical circuit diagrams showing logic circuitsforming part of the present invention,

FIG. 16 is a front elevational view of a printed circuit board used inthe machine, and

FIG. 17 is an electrical schematic diagram of the circuitry carried onthe printed circuit board of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, which best shows the general features of theinvention, the grinding machine, indicated generally by the referencenumeral 10, is shown as being of the internal grinding type, which isshown and described in the patent application of Uhtenwoldt et al., Ser.No. 676,041 filed Apr. 12, 1976. The machine is provided with a housing11 at the top of which is located a main control 13 and a size control14. A loading mechanism 15 protrudes from the upper part of the housingand covers 16 and 17 cover the operating elements of the machine.

FIG. 2 shows a feed mechanism 18 which includes a block 19 and a bearing21 which are moved up and down vertically by a stepping motor 22. Thismotor is operated by means of a ball screw 23 and a nut 24, the axis ofthe ball screw being indicated by the line C--C in the drawing. Thisline C--C is perpendicular to a horizontal plane passing through theaxes A--A of a primary bar 25 and B--B of a secondary bar 26. The block19 with its bearing 21 (which is of the hydrostatic type) is mounted onthe secondary bar 26. The stepping motor 22 has a worm 27 connected toits shaft, which worm, in turn, drives a worm gear 28. The ball screw 23engages the nut 24 in the well-known manner and serves to move the block19 vertically, thus carrying the secondary bar 26 with it. The block isattached to the nut by a connection 29 which is relatively narrow incross-section at a location between the nut and the bearing to permit aslight bending to allow a slight angular misalignment of the block 19relative to the ball screw 23 and the nut 24. This is necessary becauseof the fact that, as the wheelhead table 31 swings about the axis A--Aof the primary bar 25, it carries the secondary bar with it. The axisB--B of the secondary bar moves in a broad arc and this means that thebar and the block also move slightly horizontally relative to the centerline or axis C--C of the ball screw. This figure of the drawing alsoshows the wheelhead 33 mounted on the wheelhead table 31 and driven byan electric motor 34, all of the mechanism being mounted on a base 32 inthe usual way.

Referring next to FIG. 3, it can be seen that the grinding machine isprovided with a number of hydraulic cylinders and with valves forcontrolling the cylinders in a more-or-less conventional manner. ACLAMPING cylinder 35 operates a clamp for the workpiece 43 (FIG. 6) andis controlled by a solenoid valve 37. A hydraulic motor 38 operates anoscillator and is controlled by a solenoid valve 39. A hydraulic motor41 serves to operate a dresser 42 (FIG. 6) which is normally mounted onthe workhead table (not shown). A DRESSER cylinder 44 serves to move thedresser up and down from operative to inoperative position. The movementof the cylinder 44 as well as the actuation of the DRESSER motor 41 iscontrolled by a solenoid valve 45. A RETRACTION cylinder 46 serves towithdraw a gage 47 from the work on occasion and its operation iscontrolled by a solenoid valve 48. A TABLE cylinder 49 is built into theprimary bar 22 (not shown in this view) and serves to move that bar(along with the table 31) longitudinally of the axis A--A. The cylinder49 is controlled by a solenoid valve 51. A LOADING ARM cylinder 52 and aSHUTTLE cylinder 53 operates as part of the loading mechanism 15(FIG. 1) in a conventional manner to introduce unfinished workpiecesinto the work area and to remove finished workpieces. These last twocylinders are controlled by a solenoid valve 54. A pump 55 driven by amotor 56 is shown as supplying the hydraulic system with pressure fluidfor most of the cylinders. A separate air source is connected to theCLAMPING cylinder 35 for unclamping the workpiece and a low pressuresource of oil mist is also connected to that cylinder for lubricationpurposes.

FIG. 4 shows the manner in which the main control 13 consists of aplurality of printed circuit boards 57 mounted vertically in a housing58. These boards are connected by ribbon cables 59 and 61 to a door 62,which is hingedly mounted along one side to the housing 58 and whichcarries the display elements shown in FIG. 1.

FIG. 6 shows in a very general way the interrelation during the grindingoperation of the workpiece 43 with a grinding wheel 63 mounted on thewheelhead 33 and their relationship to the dresser 42. This view shows,particularly well, the so-called "diamond clearance" which is thedistance between the operative line of the dresser, such as the surfaceof a diamond wheel 64, and the surface 65 of the workpiece 43. Thesurface 45 which is to be finished by the grinding operation is asurface of revolution and in the drawing is shown as being cylindrical.While the dresser 42 is shown as having a diamond wheel 64 driven by themotor 41 (FIG. 3) for the purposes of description, it will be understoodthat the dressing can take place by use of a single-point diamond. Ineither case it is capable of being moved from operative to inoperativeposition by the DRESSER cylinder 44. Although the movement of theabrasive wheel relative to the diamond and the workpiece is performed bythe mechanical apparatus shown in FIG. 2, nevertheless, the feedingoriginates in the stepping motor 22 which, in turn, is controlled by themain control 13. This main control is largely made up of logic circuitryof the type shown in the patent of Robillard U.S. Pat. No. 3,867,794which issued on Feb. 25, 1975 to which reference may be made fordetails. Certain additions and substitutions are made to the circuitryshown in this last-named patent and these changes are the subject of thepresent invention. For that reason, FIGS. 9-17 show various aspects ofthe circuitry which will be useful in describing and showing the presentinvention. Because of the difficulty of placing all of the circuitry onone sheet of drawings, suitable reference numerals have been providedfor showing the interconnection of the electrical lines in one figure ofthe drawings to those of another.

In FIG. 7 is shown electrical circuitry which contains a DRESS CLEARANCEcounter 66, containing an ADD coil 67, and a SUBTRACT coil 68. A FEEDMODE line 69 enters the circuitry, as well as a FEED RESET line 71. TheDRESS CLEARANCE counter 66 is a three-digit, bi-directional,electro-mechanical counter with an electrical readout of each digit. Thecoils 67 and 68 receive their operating pulses from a DRIVER board 72(FIG. 8). An OUTPUT 1 line 73 and OUTPUT 2 line 74 are connected tocorresponding lines in FIG. 9. Signal lines 75 and 76 leading from theDRESS CLEARANCE counter 66 are connected to corresponding lines in FIG.8 and, therefore, to the DRIVER board 72. Lines 75-89 are connected tocorrespondingly-numbered lines in FIG. 8.

Entering FIG. 8 are DRESS CLEARANCE LARGER line 91, DRESS CLEARANCESMALLER line 92, DRESS CLEARANCE SET-UP line 93, and DRESS CLEARANCEAUTO line 94. These operate through the DRIVER board 72 and through thelines 75, 76, and 70 to operate the DRESS CLEARANCE counter 66. Alsoentering the circuit in FIG. 8 is a FEED RESET line 95, a FEED COUNTER 0line 96, and a FEED MODE line 97. Also entering the circuit in FIG. 8 isa TIMER START line 98, a FEED SET-UP MODE line 99, an INDEX OUT line100, an INDEX IN line 101, an INDEX SET PULSE line 102, and a DIAMONDSET PULSE line 103. As has been mentioned above, the line 70, as well asthe line 75 and 76 and the line 75-89 are connected to the circuitry ofFIG. 7. Included also in the circuitry of FIG. 8 is a PULSER TIMER board104 and a DIAMOND WORN OUTPUT line 105. Extending from the circuitry asoutput lines is a SET 800 line 106, a SET 400 line 107, a SET 200 line108, a SET 100 line 109, a SET 80 line 110, a SET 40 line 111, a SET 20line 112, and a SET 10 line 113, an INDEXED OUT line 114, a SET 1 line115, and a MASTER RESET line 116.

In FIG. 9 the input lines are shown consisting of INDEXED OUT line 73and INDEXED IN line 74. Located in this circuit is a dual 15-volt powersupply 117 connected to a voltage regulator 118. Included in thecircuitry is a DRIVEN potentiometer 119, a NEW WHEEL potentiometer 120,a WHEEL SIZE potentiometer 121, and a WHEEL WEAR potentiometer 122. Thecircuit includes a digital readout including a meter 122. An amplifier123 receives the signal from the potentiometer 119. The outputs of thepotentiometers 120, 121, and 122, as well as the output of the amplifier123, are fed into comparators 124-128 and their outputs are connected toother parts of the circuit, as will be described. The INDEXED OUT line73 is connected to a FEED AND INDEXED RESET lamp 129. The INDEXED INline 74 is connected to an INDEXED IN lamp 130. Also included in thecircuit is a SECOND SIZE/LATE GAGE lamp 131, a FIRST SIZE/EARLY GAGElamp 132, and a GAGE RELEASE lamp 133. The comparator 124 is connectedto a SET-UP CENTERING lamp 134. The comparator 125 is connected to a NEWWHEEL lamp 135. The comparator 126 is connected to a WHEEL SIZE lamp136. The comparator 127 is connected to a WHEEL WEAR lamp 137. Theselamps 129-137 are all located on the door 62 of the main control 13 (seeFIG. 1).

Referring now to FIG. 10, a set of input lines, including the lines98-103, are connected to the corresponding lines in the circuit of FIG.8. The circuit includes a RETRACTION IN line 138 and a COARSECOMPENSATION line 139, as well as a COMPENSATION (FEED DIRECTION) line140, as well as a RETRACT line 141. Also entering the circuit is anAUXILIARY RETRACTION line 142, a RETRACTION line 143, a FEED SET-UP line144, a FEED AUTOMATIC line 145. Also entering the circuit is a ROUGHRATE line 146, a FINISH RATE line 147, and a GAP ELIMINATOR RATE line148. Connected into the circuit is a RETRACTION "IN" PULSE line 149 anda FEED RATE line 150. Lines 150-164 are connected to correspondinglynumbered lines in the circuit of FIG. 11. Line 165 is also connected toa similar numbered line in FIG. 11. Also included in the circuit of FIG.10 are the operating coils of relays 3RR, 4RR, 5RR, 6RR, 7RR, and 8RR.

In FIG. 11 the DRESS CLEARANCE counter 66 is shown again in a differentsetting and is shown as connected to a three decade down-counter 166.Also included in the circuitry is a linear-resistance-controlled clock167. A ROUGH RATE digiswitch 168 and a FINISH RATE digiswitch 169 areshown as connected to the counter through line 170 and 171,respectively. A printed circuit board 172 is shown as containing aMANAGEMENT CONTROL function, as well as a COMPENSATION AND RETRACTIONsection. The lines 150-165 are shown as entering the circuitry of FIG.11 from the circuitry of FIG. 10. The line 150a is connected to theDRESS CLEARANCE counter 66. Line 161 is connected to a COARSECOMPENSATION thumb-wheel switch 173. Line 152 is connected to a STANDARDCOMPENSATION thumb-wheel switch 174, while the line 154 is connected toa RETRACTION thumb-wheel switch 175. At the upper part of the drawingcan be seen the lines 106-113 and line 115 which are connected tosimilarly-numbered lines in the circuit of FIG. 8. Extending from thecircuitry of FIG. 11 are a HANDPICK "OUT" line 176, a FEED RESET COMMANDline 177, a FEED COMMAND line 178, a TIMER START line 179, an INDEXCOUNTER RESET line 180, and a CLOCK #4 line 181. Also included in thecircuit is a SAFETY timer 182. Extending out of the circuit are lines183-189 which connect to correspondingly-numbered lines in FIG. 12. Alsoline 190 extends from the circuitry into the circuitry of FIG. 12.

FIG. 12 shows the stepping motor 22 and associated equipment. A DRIVERboard 191 connected to the motor and back to a PULSE-TO-STEP CONVERTERboard 192. Into the circuit of FIG. 12 enters the MASTER RESET line 116from the circuit of FIG. 8, as well as the lines 183-190 from thecircuit of FIG. 11. Into the circuit also extends a FEED LIMIT line 193,a RETRACT limit line 194, and a 200-STEPS-PER-REVOLUTION MODE line 195.Leaving the circuit is a CLOCK #2 line 196, an INDEX CLOCK INHIBIT line197, and a MASTER RESET line 198.

FIG. 13 shows a MASTER RESET timer 199 and entering the circuit a ROUGHSIZE OVERRIDE line 200, and a FINISH SIZE OVERRIDE line 201. Enteringthe circuit from the circuit of FIG. 8 are the FEED RESET line 95, theFEED COUNTER 0 line 96, and the FEED MODE line 97. Entering the circuitfrom the circuit of FIG. 10 is the RETRACTION "IN" PULSE line 149, andthe FEED RATE line 150. Entering the circuit from the circuit of FIG. 11is the HAND-PICK "OUT" line 176, the FEED RESET COMMAND line 177, theFEED COMMAND line 178, the TIMER START line 179, the INDEX COUNTER RESETline 180, and the CLOCK #4 line 181.

Leaving the circuit of FIG. 13 and entering the circuit of FIG. 14 arelines 202-208 and 211-215. Leaving the circuit of FIG. 13 and connectedto correspondingly numbered lines in the circuit of FIG. 15 are thelines 216, 217, and 218.

FIG. 14 contains a THREE-DECADE UP-DOWN COUNTER board 219 and aTHREE-DECADE COMPARATOR BOARD 220. Entering the circuit is a DIVIDE BY"2" OFF line 221 and a MEMORY RESET line 222. As has been stated above,lines 202-208 and lines 211-215 enter the circuit of FIG. 14 from thecircuit of FIG. 13. Connecting the circuit of FIG. 14 to the circuit ofFIG. 15, are lines 223 through 241.

Referring now to FIG. 15, it can be seen that the circuit includes aMANAGEMENT CONTROL board 238 containing a FEED POSITION section. It alsoincludes a SECOND SIZE/LATE GAGE thumb-wheel switch 239, a FIRSTSIZE/EARLY GAGE thumb-wheel switch 240, a GAGE RELEASE thumb-wheelswitch 241, and a three-digit readout 242. Entering the circuit of FIG.15 from the circuit of FIG. 13 are the lines 216, 217, 218, as well aslines 223-241. Also entering the circuit from the circuit of FIG. 8, isthe INDEXED OUT line 114. Entering the circuit from the circuit of FIG.12 are the CLOCK #2 line 196, the INDEX CLOCK INHIBIT line 197 and theMASTER RESET line 198. Leaving the circuit is a FEED COUNTER ZERO line243, FEED AND INDEX RESET lines 244, 245, and 246, SECOND SIZE/LATE GAGElines 247, 248, and 249, FIRST SIZE/EARLY GAGE lines 250, 251, and 252,and GAGE RELEASE lines 253, 254, and 255. Also carried in this circuitare the coils of relays 9RR, 10RR, 11RR, 12RR, and 13RR.

Referring next to FIG. 16, which shows a PULSER TIMER board 256, it isshown as carrying reed relays 1RR, 2RR, 3RR, and 4RR, as well as avoltage-to-frequency converter 257.

FIG. 17 is a schematic showing the electrical circuitry used on theboard 256. The circuit includes a dual operational amplifier 258 which,if the voltage on an input connection goes above a preset reference(junction of R-11 and R-19) it shorts out the OUTPUT PULSE from 257,STOPPING THE CLOCK.

It can be seen, then, that the grinding machine 10 is intended forgenerating a surface of revolution 65 on a workpiece 43. The machine isprovided with a base 32 on which are mounted a workhead carrying theworkpiece 43 and a wheelhead 33 carrying the abrasive wheel 63. Theworkhead and the wheelhead are mounted on the base for relative movementlongitudinally and transversely of the axis of the surface of revolution65. A stepping motor 22 is operative to produce the said transverserelative movement in the response to the arrival of electrical pulsesfrom the driver board 191. A pulse generator in the form of the clock167 is connected to the stepping motor 22 to supply the said electricalpulses by way of the pulse-to-step converter board 192. Resistance units168 and 169 connected to the PULSE GENERATOR clock 167 serve to controlthe frequency of the pulses. The selector digi-switches 168 and 169 eachinclude an actuator which is movable in physical increments to connectequal increments of resistance to the clock 167. The said increments ofresistance produce equal increments of frequency of the pulses emittedfrom the clock. The operational amplifier 258 (FIG. 17) provides acircuit which reduces the pulse frequency to "zero" when an open circuitaccidentally incurs in the resistance units, thus preventing the machinefrom "running away". A circuitry provides a straight-line relationshipbetween the amount of resistance connected in the resistance units 168and 169 and the frequency of the pulses emitted by the clock 167 for theoperation of the stepping motor. The units 168 and 169 are commerciallyavailable thumb-wheel digital switches associated with a plurality offixed resistances.

It is clear also that a dresser 42 is provided, carrying a dressingelement 68 which is mounted on a portion of the machine which is notsubject to transverse motion relative to the workhead and the workpiece43. Means is provided for generating a signal indicative of the locationof the operative surface of the dresser, this means consisting of thegage 47 and the measuring mechanism to determine whether the workpiecereaches FINAL SIZE before or after a predetermined time. The signalsindicative of this fact are impressed on the lines 91 and 92 (in FIG. 8)to operate the DRESS CLEARANCE counter 66. A means consisting of thecounter 168 serves to introduce a selected number of pulses to thestepping motor 22 to produce an original DIAMOND CLEARANCE movementbetween the workpiece and the abrasive wheel, while the DIAMONDCLEARANCE counter 66 serves to convert the signal on the lines 91 and 92to a series of pulses and adding them algebraically to the selectednumber of pulses in the original diamond clearance, so that the DIAMONDCLEARANCE movement serves to bring the dressed surface of the wheel 63to the same point relative to the workpiece 43 after each dressingoperation. The means generating the signal is the gage 47 which operateson the surface 65 of the workpiece 43 during the grinding operation and,particularly, during the finish portion thereof. The counter 166, whichintroduces a selected number of pulses to the feed means for grinding,is a three-digit, bi-directional electro-mechanical counter with anelectrical readout of each digit. A diode board is attached to thecounter 66 to convert the three-digit readout to a three-digit BCDreadout. A WORN DIAMOND signal is generated, when the results of thealgebraic addition falls below a predetermined value. This serves toilluminate the WHEEL WEAR lamp 137, and it also acts to shut down thegrinding machine.

The operation of the grinding machine will now be readily understood inview of the above description. The movement of the grinding wheel 63relative to the workpiece 43 and its surface 65 which is to be finishedtakes place in the present embodiment of the machine entirely bymovement of the wheelhead 33. The workhead on which the workpiece 43 ismounted is maintained in a fixed position. The motion of the wheelhead33 takes place by sliding the wheelhead table 31 along the bar 25 (FIG.2) and this longitudinal motion is produced by use of the TABLE cylinder49 in FIG. 3 and the OSCILLATOR motor 38. When the operator starts upthe machine, the wheelhead motor 34 is energized and rotates theabrasive wheel 63 in the usual way. The dresser 42 at the beginning ofthe cycle is normally in "raised" position and is lowered on occasion bythe cylinder 44. In the preferred embodiment, the dresser is a rotatabledressing wheel 64 studded with diamonds, which wheel is rotated by theDRESSER motor 41. Loading of the workpiece takes place, of course, bymeans of the LOADING ARM cylinder 52 and the SHUTTLE cylinder 53 andtakes place through the loading mechanism 15. The operator sets thedigital switches and other controls on the face of the door 62 whichforms part of the main control 13. The crossfeed movement between thewheel 63 and the workpiece 43, as well as relative to the dresser 42,takes place by presenting negative and positive pulses to the steppingmotor 22, so that it moves the bar 26 up and down along the line C--C ofFIG. 2. This movement, in turn, produces a singing movement of thewheelhead 33 and of the abrasive wheel 63 carried thereby in a shallowarc, which is substantially a horizontal transverse movement.

The operation of the grinding cycle will be explained in connection withFIG. 5. With the table 31 and the wheelhead 33 at an extreme right-handposition away from the workpiece 43, the cycle begins at the point A.The wheelhead is moved longitudinally inwardly and, when loading of thenew workpiece has been completed, the wheelhead has reached the point B.At the point C the longitudinal motion ceases and pulses are presentedto the stepping motor 22 to cause the wheelhead to move rearwardly ofthe machine toward the surface 65 of the workpiece. It does so at a veryrapid rate until a point D is reached. A slower rate of movement of thewheel toward the workpiece begins with a conventional load metermeasuring the current passing to the wheelhead. When the wheel makescontact with the surface 65 of the workpiece, the current on thewheelhead motor rises suddenly and the load meter operates in thewell-known manner to cause a shift in feed rate to a slower value. Inthis case, a coarse feed rate is selected wherein the pulses presentedto the stepping motor 22 are at a relatively slow rate compared to therate of motion from the point C to the point D and from the point D tothe point E. Grinding takes place at this slow rate until the gage 47indicates that a FIRST SIZE has been reached, this taking place at thepoint F. Reverse pulses are presented to the stepping motor 22 and thewheel backs off at a very rapid rate on a RETRACTION movement to thepoint G. Pulses continue to be presented to the stepping motor to causeit to move further forward of the workpiece surface 65 unitl the point His reached. The table 25 is then moved longitudinally by the TABLEcylinder 49 and then is moved rearwardly on a COMPENSATION movement fromthe point I to the point J. At that time the TABLE cylinder moves thetable and the wheelhead inwardly again to the left so that the wheelpasses over the dresser 42, which in the meanwhile has been moved intooperative position by the cylinder 44. The DRESSER motor 41 rotates thedresser wheel in the usual way. As the wheel passes over the dresserelement 64, a small amount of the surface of the wheel is removed torenew the surface to make it "sharp".

The dress is completed by the time the point K has been reached and, atthe point L, the grinding wheel 65 lies entirely within the bore of theworkpiece, that is to say, is co-extensive with the surface 65. At thattime, pulses are presented to the stepping motor 22 to advance it towardthe workpiece surface at a rapid rate. The number of pulses isdetermined by the count in the counter 166, as adjusted by the amount ofthe count in the DRESS CLEARANCE counter 66. Feed takes place to thepoint M, at which time the count in the counter 219 in FIG. 14 takesover and determines the amount of movement of the wheelhead toward theworkpiece from that point on for a grinding portion of the cycle. Therapid rate pulses continue to be presented to the stepping motor 22, sothat the wheelhead advances still further at which time the memoryoutput causes the rate of pulses to be switched over to a fine rate offeed, this taking place at the point N. The fine or FINISH RATE feedingtakes place from the point N to the point O, at which time the gage 47indicates that a SECOND PREDETERMINED SIZE has been reached in theworkpiece. From the point O to the final point P, the grinding takesplace by "spark-out" in which the deflection in the spindle on which thegrinding wheel is mounted serves as the only mechanism for advancing thewheel toward the workpiece. The gage indicates that the third and FINALSIZE has been reached and it acts to present reverse movement pulses tothe stepping motor 22 to move the wheel away from the finished workpiecesurface. The measuring mechanism indicates whether the point P has beenreached during a NORMAL GAGE ZONE, or whether the point P lies in a LATEGAGE ZONE, the nature of this location of the final point P determiningthe presence of a signal on the lines 91 or 92 or the entire absencethereof. If the point P is reached in the EARLY GAGE ZONE, this meansthat the diamond 64 is worn, so that, when the grinding wheel isdressed, it dresses the wheel too large. In order to overcome this, itis necessary to change the amount of the DRESS CLEARANCE to make itlarger, so that the wheel (when dressed) will not reach final size untila later time and so that the point P appears in the NORMAL GAGE ZONE.If, on the other hand, the point P appears in the LATE GAGE ZONE, it isindication that thermal changes or the like have taken place in themachine and that the diamond is located too far toward the front of themachine. It is then necessary to send a signal on the line 92 tosubstract from the count in the DRESS CLEARANCE counter 66 and tocompensate for this discrepancy from standard conditions.

It can be seen, then, that since the DIAMOND CLEARANCE dimensiondetermines when the points D, G, and M are reached. Wear and thermalchanges in the location of the operative surface of the dresser can, onthe one hand, cause the rapid infeed to be slowed too early in the cyle(in which case machine time is wasted) or it can be reached too late inthe cycle in which case the grinding wheel is likely to be damaged byrough contact at high speed with the surface of the workpiece.

The present invention makes it possible also to set the ROUGH RATE andthe FINISH RATE by means of the digital switches 168 and 169 in such away that the frequency of the pulses, as presented to the stepping motor22, is in exact accordance with the count showing on the digiswitch. Itis not necessary to calibrate the digiswitch, but the exact readout onthe digiswitch can be used to determine the frequency. This is becausethe linear resistance control clock 167 gives a frequency of pulses thatbears a straight line relationship to the settings on the switches 168and 169. This is all accomplished by the operation of the circuitryshown in FIG. 17 and the voltage-to-frequency converter 257. Theoperational amplifier 258, as has been stated, serves to stop themachine if an electrical open circuit takes place in the rate settingcircuitry which includes the digiswitches 168 and 169. It should bepointed out that the position of the wheelhead relative to the point Dand M is always indicated on the face of the main control 13 and itsposition is determined by the counter 219 in FIG. 14. The pulses thattake place in the parts of the cycle below the level of these points(forward of the workpiece surface) is carried in the counter 166 andconstitutes the "DIAMOND CLEARANCE", as has been described above. Theuse of the present invention means, therefore, that, irrespective of thephysical location of the points D and M, the readout on the feed counter219 is zero at that point, so that the operator need not be concernedwith the fact that the internal construction of the machine provides thecompensation for the diamond wear and like variations in diamond surfacelocation.

The advantages of the present invention will now be readily understoodin view of the above description. With this invention it is possible touse the commercially-available digi-switches for setting the feed rateand, at the same time, be assured that the setting on these switchesproduces an accurate rate of feed. Since the digiswitch presentsdiscrete amounts of resistance, the amounts depending on the setting andthe showing of the switches, it is desirable (but was not available inthe prior art devices) to have the rate be actually commensurate withthat setting. This has been accomplished by the present invention. Inother words, the rate of feed is controlled in the present device bymeans of an external resistance which can be set by the operator on theface of the main control and this rate is directly proportional to thevalue of the resistance thus set. In a commercial version of themachine, the board was set in such a way that a resistance change of 10ohms resulted in a change in the pulsing rate of 1 hz. The range of thepulsing circuit was from 1 hz. to 1,000 hz. with a change in resistancefrom 10 ohms to 10,000 ohms. In connection with the DIAMOND CLEARANCEcounter system, the commercial version of the invention was providedwith a commercial three-digit, bi-directional electro-mechanical counterwith an electrical readout of each digit. A diode board was attached tothis counter in order to convert the ten-line three-digit readout to athree-digit BCD readout. Two additional circuit boards required for thissystem plugged into the main control printed circuit board rack. Thesetwo boards were the DIAMOND INDEX LOGIC board and the COUNTER CONTROLboard. The main purpose of the electro-mechanical counter is to providesomething that will accept signals and compensate for "drift" due todiamond wear, thermal effects, and the like. These signals came from astandard feedback circuit which used an "EARLY GAGE" or a "LATE GAGE"signal to indicate drift. On other types of machines an after-gagesystem might be used to provide this feedback signal.

The counter, incidentally, also gives a visual indication of theclearance between the diamond point and the surface of the ungroundworkpiece. This indication is a three-digit decimal readout, each digithaving a value of 0.0001 inches on the diameter. In the commercialversion of the machine, this means that a counter setting of "100" willindicate a diamond clearance of 0.010 inches on diameter (0.005 inchesactual). The electrical readout of this counter is used in much the samemanner as a three-digit thumb-wheel switch. It presets a number on adowncounter to index the wheel to and from the work. At the start of thegrinding cycle, the wheel is indexed toward the work by a number ofpulses equal to the counter setting. This index is not displayed on thedigitial readout of the feed, as has been stated above, but is indicatedby an "INDEXED IN" lamp 130 when the index has been completed (at thepoint O or the point M). At this time the wheel is further advancedtoward the work at a rapid rate until the load meter signal is obtained.The load meter contact changes this rapid rate to the rough grindingrate and the grinding cycle continues in the same way as with anystandard stepping motor feed grinding machine.

All of the feed which takes place from the "INDEXED IN" position (pointD) is displayed on the digital readout of the feed on the face of themain control 13, so that the operator can see it. When "final size" isreached, the feed is first reset to zero, which will be indicated on thedigital readout. Once the feed reaches zero, the wheel is "indexed out"again by the amount of pulses equal to the electro-mechanical countersetting. This position is indicated by a FEED AND INDEXED RESET light129. A relay is also energized at this time and its contacts are usedfor cycle sequencing. From this description, it can be seen that thetotal in-feed of the grinding wheel consists of two separate motions ofthe stepping motor. These are first the "index" (which is not displayedon the feed readout) but does accept feedback. The second is thestandard feed that does display on the readout and has electricaloutputs at preset positions. It can be seen that the overall system canbe thought of as a standard stepping motor feed with a digital type ofzero shift. This "zero shift" can be controlled from both internal andexternal in-put signals.

Another important feature of the present invention, is that it will stopthe machine when a "DIAMOND WORN" signal is generated. This signal isautomatically produced when the wheel is indexed "in" or "out" and theelectro-mechanical counter is below "010", which is 0.001 inches ondiameter. The cycle will stop at the end of the grinding cycle and alight will signal the operator that the diamond is worn. At this time,the operator will remove the diamond and inspect it. He will decidewhether the diamond should be replaced or readjusted. In either case,the operator will switch the diamond clearance counter to the "SET-UPMODE" using a three-position selector switch. Next, using thelarger-smaller spring return-to-center in the selector switch, theoperator will hold the switch in the larger position. The diamondclearance counter will now receive impulses at a rate of approximately 8hz. on the "ADD" coil 67. Each ADD impulse will retract the wheel onestep or 0.001 inches on diameter by means of the stepping motor. Whenthe operator reaches the desired diamond clearance on the counter, hewill release the selector switch, thus stopping both the counter and thegrinding wheel. If he goes beyond his desired position, he can reversethe counter and the wheel by actuating the spring return switch in theopposite direction. Once this position has been reached, the operatorwill install a new diamond or replace the old diamond. It would beadjusted manually at time in such a way that the operative dressersurface just touches the grinding wheel. Once the grinding cycle hasbeen restarted, the feedback signals may shift the counter in onedirection or the other. This would be the case if the operator was nottoo accurate in his adjustment of the diamond.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is:
 1. A grinding machine forgenerating a surface of revolution on a workpiece, comprising: p1 a. abase,b. a workhead and a wheelhead mounted on the base for relativemovement transversely of the axis of the surface of revolution, c. astepping motor operative to produce the said relative movement inresponse to receipt of electrical pulses, d. a pulse generator connectedto the stepping motor to supply the said electrical pulses, thegenerator including a resistance unit connected to control the frequencyof the pulses, the unit including an actuator movable in increments toconnect equal increments of resistance to the generator, the saidincrements of resistance producing equal increments of frequency ofpulses, and e. a circuit that reduces the pulse frequency to zero whenan open circuit occurs in the resistance unit.
 2. A grinding machine asrecited in claim 1, wherein a straight-line relationship exists betweenthe resistance in the resistance unit and the frequency of pulsesemitted by the pulse generator.
 3. A grinding machine as recited inclaim 1, wherein the resistances in the resistance unit are selected bysettings of a plurality of thumb-wheel digital switches associated witha plurality of fixed resistances.